mode-II Stress Intensity Factors Research Articles

Mode-II stress intensity factors for special-shaped cylindrical shells in torsion

Special-shaped cylindrical shells in torsion are encountered in engineering applications, which will induce the Mode-II singular stress fields next to circumferential crack tips. The Mode-II stress intensity factor (SIF) represents the strength of these singular stress fields and is an important fracture parameter. The crack problems for the cylindrical shells are typical finite boundary value issues. It is very difficult to get the exact solutions by using the classical theory of elasticity. In present article, based on the concepts of the conservation law and the elementary strength theory, a hybrid methodology to determine the Mode-II SIFs for circumferential cracked special-shaped cylindrical shells in torsion is suggested. Due to the introduction of elementary mechanics, the corresponding errors are also inevitably carried into the Mode-II SIFs. However, the finite element analysis indicates that the error of the Mode-II SIFs calculated by present method is acceptable.

Analysis of an interfacial crack between two nonhomogeneous piezoelectric materials using a new domain-independent interaction integral

Considering the difficulties introduced by piezoelectric material non-homogeneity and discontinuities to interfacial crack analysis, a domain-independent interaction integral (DII-integral) is proposed to derive the stress intensity factors (SIFs) and electric displacement intensity factor (EDIF) of an interfacial crack between nonhomogeneous piezoelectrics. For continuously varying material properties, traditional interaction integral (I-integral) needs to compute the derivatives of material parameters with respect to the x1 direction of the local coordinate system, while the proposed DII-integral is demonstrated to be unrelated to any derivatives of material parameters. Furthermore, a significant improvement is achieved that the new formulation of I-integral remains valid even when the integration domains include intricate and multiple interfaces, as long as the material interfaces are perfectly bonded. Firstly, the intensity factors (IFs) calculated by the combination of the DII-integral and the extended finite element method are compared with the analytical solutions, and it is found that the relative errors of the IFs are all less than 1.79 % with various crack lengths, which verifies the accuracy of the proposed method. For the piezoelectric bi-material model with continuously nonhomogeneous properties, the calculated IFs match each other well (relative deviation < 1.3 %) for different sizes of integration domains. In addition, for the perfectly bonded interface with discontinuous electromechanical properties, the IFs are almost identical (relative deviation < 0.85 %) whether or not the integration domain contains the material interface, which further numerically verifies the good domain-independence of the established DII-integral. For an interfacial crack near extra interfaces, the differences in elastic stiffness and piezoelectric coefficient between interface sides have an obvious influence on mode-I SIF, but mode-II SIF and EDIF are affected mainly by piezoelectric coefficient and dielectric permittivity.

Numerical modeling of crack propagation from open and closed flaws in rock

The traditional fracture criterion performs well when calculating crack propagation under tensile conditions, but a zigzag crack propagation path was obtained under compression, which is inconsistent with experimental results. This study indicates that the positive and negative oscillations of the mode-II stress intensity factor (KII) under compressive loading during crack propagation is the reason for the zigzag trajectory of crack propagation. Such oscillation of KII can be effectively eliminated when the non-singular stress (T-stress) at the flaw tips is considered, and thus, the path of crack propagation can also be smoothed. However, due to the complicated calculations of the stress intensity factors and T-stress at each step of crack propagation, it is not suitable for simulation in fast, complex environments and multi-flaws. Also, the lack of a shear fracture criterion in traditional fracture methods leads to difficulty in studying shear crack propagation in rock. Therefore, a strength-based localized maximum stress (SLMS) criterion was proposed in this study to model both tensile and shear crack propagations in rock more efficiently, conveniently, and accurately. Then, the crack propagation processes in both plate and Brazilian disc specimens with a single flaw under uniaxial and biaxial compression were modeled to investigate the effects of the flaw inclination angle, friction coefficient, and loading level on the crack propagation path. The influence of the contact friction between the flaw surfaces on the contact status and the crack propagation path during the crack propagation process was also analyzed. Also, the crack propagation in a plate with a single flaw under biaxial tension was modeled, which shows bifurcation crack propagation when the lateral tension is several times larger than the axial tension. All the modeled results indicated that the proposed SLMS criterion can get better results when modeling crack propagations for open or closed flaws under tension or compression conditions.

Crack propagation, failure and ultimate load capacity of the grout layer in the prestressed anchor bolt foundation of wind turbine tower

The finite element (FE) analyses based on linear elastic fracture mechanics (LEFM) for the crack propagation and failure of the grout layer in the wind turbine foundation with pre-stressed anchor bolts are presented. Firstly, one half-symmetric planar numerical model is developed. According to the linear elastic analytical results, one initial crack is set to be the zone of the maximum tensile streess and its direction is perpendicular to the direction of the maximum principle tensile stress. The crack will propagate in the direction of the zero mode-II stress intensity factor during the failure of the grout layer. The numerical simulations with different prarmeters are performed. The histories of mode-I stress intensity factor are analyzed and design formulas predicting the failure and ultimate load capacity of the grout layer are proposed based on parametric studies. The increasing width or the decreasing depth of the grout layer can significantly mitigate the failure. One case study of the grout layer with the typical size and the corresponding fatigue analyses are carried out. The numerical results show that the proposed equation can agree well with the cracking status and failure of the grout layer in practical engineering and help predict the fatigue life of the grout layer under the certain intial crack length.

Thermal Stressed State of a Bimaterial with Interface Crack Filled with a Compressible Liquid

We formulate the problem of thermoelasticity for a bimaterial with interface crack filled with a liquid with regard for the pressure and heat conductivity of the liquid. We consider the case of partial crack closure on the edges under the action of a compressive load and a heat flux. The problem is reduced to a system of nonlinear singular integrodifferential equations for a temperature jump between the crack faces and its opening displacement. The length of the contact zone is determined from the condition of smooth closure of crack faces at the points separating the open and closed parts of the crack. We analyze the changes in the crack length and height and in the pressure of liquid depending on the compressive loads, density of the heat flux, and its direction. We also determine the dependence of the mode-II stress intensity factor on the level of pressure and the thermal conductivity coefficient of liquid.

A generalized machine learning framework for brittle crack problems using transfer learning and graph neural networks

Despite their recent success, machine learning (ML) models such as graph neural networks (GNNs), suffer from drawbacks such as the need for large training datasets and poor performance for unseen cases. In this work, we use transfer learning (TL) approaches to circumvent the need for retraining with large datasets. We apply TL to an existing ML framework, trained to predict multiple crack propagation and stress evolution in brittle materials under Mode I loading. The new framework, ACCelerated Universal fRAcTure Emulator (ACCURATE), is generalized to a variety of crack problems by using a sequence of TL update steps including (i) arbitrary crack lengths, (ii) arbitrary crack orientations, (iii) square domains, (iv) horizontal domains, and (v) shear loadings. We show that using small training datasets of 20 simulations for each TL update step, ACCURATE achieved high prediction accuracy in Mode-I and Mode-II stress intensity factors, and crack paths for these problems. We demonstrate ACCURATE’s ability to predict crack growth and stress evolution with high accuracy for unseen cases involving the combination of new boundary dimensions with arbitrary crack lengths and crack orientations in both tensile and shear loading. We also demonstrate significantly accelerated simulation times of up to 2 orders of magnitude faster (200x) compared to an XFEM-based fracture model. The ACCURATE framework provides a universal computational fracture mechanics model that can be easily modified or extended in future work.

A Domain-Independent Interaction Integral for Dynamic Fracture in Nonhomogeneous Magneto-Electro-Elastic Materials

In practice, magneto-electro-elastic (MEE) equipment are inevitably subjected to impact loading during service, resulting in fracture failure of the devices. This paper proposes a dynamic domain-independence interaction integral (DII-integral) to solve the dynamic intensity factors (IFs) at the crack tip of MEE materials. Here, this is a new expression of the interaction integral (I-integral) for dynamic crack study of nonhomogeneous MEE media, and we further extend it to MEE materials containing complex interfaces. Domain-independent property of the I-integral is theoretically demonstrated and excellent numerical results (relative deviation<1%) obtained from the various integration domains again verify the domain-independence for nonhomogeneous and multi-interface material properties without considering the material continuity requirements. Through the combination of the DII-integral and extended finite element method (XFEM), a good agreement is observed by comparing with the published data subjected to different MEE impact loadings. Typical examples reveal that the magnitude of dynamic mode-I stress intensity factor (SIF), dynamic electric displacement intensity factor (EDIF) and dynamic magnetic induction intensity factor (MIIF) decrease with the increase of the poling angle of the MEE material, while the dynamic mode-II SIF shows the opposite change. The peaks of dynamic EDIF and MIIF are more sensitive to the distance between the parallel cracks than the SIF, and all IFs are smaller than single crack due to the shielding effect. Finally, the significant difference on the dynamic IFs is observed with various material discontinuities.

Mixed-mode dynamic fracture parameters for soda-lime glass

Dynamic mixed-mode fracture of soda-lime glass (SLG) was experimentally investigated using a full-field optical method - Digital Gradient Sensing (DGS) - in conjunction with ultrahigh-speed photography. Single edge-notched specimens were subjected to reverse impact loading using a modified Hopkinson pressure bar. The specimens were eccentrically loaded at different offset distances relative to the initial notch to achieve a wide range of mode-mixities, from mode-I to nearly mode-II condition, at initiation. Two time-resolved orthogonal angular deflection fields of light rays proportional to the respective full-field stress gradients were optically measured during experiments on different geometries. Mode-I and -II stress intensity factor histories spanning pre- and post-initiation behaviors were evaluated via over-deterministic least-squares error minimization of optically measured full-field data. By considering the critical stress intensity factors at different crack initiation modes, a fracture envelope for SLG encompassing various mode-mixities was developed for the first time for SLG and compared with predictions from prevailing approaches. An empirical fit of data seems to capture the overall trend whereas the prevailing methods do not. Measured crack kink angles are compared with the popular MTS and SED fracture criteria; both predict the kink angles reasonably well. Unlike brittle polymers, the critical effective stress intensity factors for SLG are independent of mode-mixity over a large range of values but show a decreasing trend as mode-II conditions become dominant and an extrapolated critical mode-II stress intensity factor of 0.37 MPa√m, approx. one-half of its mode-I counterpart, is seen.

An Interval Fracture Analysis Method for Cracked Structures with Unknown-But-Bounded Parameters

Abstract An interval fracture analysis method based on the Taylor expansion is presented to predict the stress intensity factor (SIF) bounds for cracked structures with unknown-but-bounded parameters. Traditional probabilistic fracture analysis requires numerous sample points, because large errors will occur when the probability density distribution function of the parameters cannot be described by sufficient sample points. In the present paper, the expression of the SIF crack structure is given using the quarter-point displacement method. Then, the interval expressions of mode-I and mode-II SIF are obtained using the Taylor expansion and the interval finite element method, and the upper and lower limits of an equivalent SIF (ESIF) are determined. Finally, the new method is analytically compared with the interval Monte Carlo method. Numerical examples show that the influence of load uncertainty considerably surpasses that of the dimension uncertainty. The mode-I SIF has a greater impact on the ESIF. As the uncertain level increases, the accuracy of the upper and lower limits of the ESIF calculated by the new method is maintained at a high level.

Initiation and Fracture Characteristics of Different Width Cracks of Concretes under Compressional Loading

A stress concentration at a crack tip may cause fracture initiation even under low-stress conditions. The maximum axial stress theory meets the challenges of explaining the fracture propagation of a non-closed fracture of cracked concretes under compressional loading. Uniaxial loading tests of single-crack concrete specimens were carried out and a numerical simulation of fracture propagation under uniaxial compression was performed. The radial shear stress criterion for a mode-II fracture is proposed to examine the stress intensity factor (SIF) of the pre-crack specimens under compressional loading. When the maximum radial shear stress at the crack tip is larger than the maximum axial tensile stress, and the maximum dimensionless SIFs can satisfy frθmax/fθmax &gt; 1 and frθmax/fθmax &gt; KIIC/KIC (fθmax=KIe/σyπa and frθmax=KIIe/σyπa are maximum dimensionless mode-I and mode-II SIFs, respectively), the crack will extend along the direction of the maximum radial shear stress. The influence of the single-crack angle and width on the mechanical properties of the specimens was examined. The experimental and numerical results indicate that the existence of cracks can considerably weaken the strength of the specimen. The distribution and width of the cracks had a significant effect on the specimen strength. The strength of the concrete specimen initially decreased and then increased with increasing fracture angle. The failure mechanism and rupture angle of pre-crack brittle material while considering crack width will be discovered.

Graph neural networks for simulating crack coalescence and propagation in brittle materials

High-fidelity fracture mechanics simulations of multiple microcracks interaction via physics-based models can become computationally demanding as the number of microcracks increases. This work develops a Graph Neural Network (GNN) based framework to simulate fracture and stress evolution in brittle materials due to multiple microcracks’ interaction. The GNN framework is trained on the dataset generated by XFEM-based fracture simulator. Our framework achieves high prediction accuracy on the test set (compared to an XFEM-based fracture simulator) by engineering a sequence of GNN-based predictions. The first prediction stage determines Mode-I and Mode-II stress intensity factors (which can be used to compute the stress evolution by LEFM), the second prediction stage determines which microcracks will propagate, and the final stage actually propagates crack-tip positions for the selected microcracks to the next time instant. The trained GNN framework is capable of simulating crack propagation, coalescence and corresponding stress distribution for a wide range of initial microcrack configurations (from 5 to 19 microcracks) without any additional modification. Lastly, the framework’s simulation time shows speed-ups 6x–25x faster compared to an XFEM-based simulator. These characteristics, make our GNN framework an attractive approach for simulating microcrack propagation and stress evolution in brittle materials with multiple initial microcracks.

On thermoelastic analysis of two collinear cracks subject to combined quadratic thermo-mechanical load

This paper addresses problem of two collinear cracks in an infinity orthotropic solid subject to combined thermal and mechanical loads. Based on a model called ' improved partially conductive crack model', the Fourier transform and superposition theorem, the analytical solutions to some physical quantities and fracture parameters are given. It is revealed that the dimensionless thermal resistance (Rc) between the upper and below crack regions and the proposed coefficient (ε) exert a great influence on some physical quantities and fracture parameters, i.e., the mode-II stress intensity factors (KII) by numerical results.

Mixed-mode cohesive laws and the use of linear-elastic fracture mechanics

Small-scale cohesive-zone models based on potential functions are expected to be consistent with the important features of linear-elastic fracture mechanics (LEFM). These include an inverse-square-root K-field ahead of a crack, with the normal and shear stresses being proportional to the mode-I and mode-II stress-intensity factors, KI and KII, the work done against crack-tip tractions being equal to KI2+KII2∕Ē, where Ē is the appropriate modulus, and failure being controlled by the toughness. The use of an LEFM model also implicitly implies that the partition of the crack-tip work into shear and normal components is given by a phase angle defined as ψK=tan−1KII∕KI. In this paper, we show that the partition of crack-tip work in a cohesive-zone model is consistent with LEFM if the normal and shear deformations across an interface are uncoupled. However, we also show that this is not the case for coupled cohesive laws, even if these are derived from a potential function. For coupled laws, LEFM cannot be used to predict the partition of work at the crack tip even when the small-scale requirements for LEFM conditions being met; furthermore, the partition of the work may depend on the loading path. This implies that LEFM cannot be used to predict mixed-mode fracture for interfaces that are described by coupled cohesive laws, and that have a phase-angle-dependent toughness.

Stress intensity factor and interaction analysis of offset parallel cracks in brittle solids

The analytical solutions for the mode-I and mode-II stress intensity factor (SIF) of arbitrary distributed offset parallel cracks in brittle solids were generated based on the Kachanov method and superposition principle. By analyzing the SIF ratio, effects of the horizontal interval, vertical interval, crack inclination angle and crack length on the interaction of offset parallel cracks were estimated, and the interference area of the crack was determined theoretically. Numerical models were established using the finite element method (FEM) to show the performance of the present method, and the relationship between crack propagation and crack interaction was discussed. The results show that the SIFs obtained from the present method agree well with the accurate ones. The interaction of offset parallel cracks contains three types, i.e. reinforcing effect, shielding effect and null-effect, which can convert mutually with the change in interval, crack inclination angle and crack length. The interference area of the crack can be divided into reinforcing, shielding area and null-effect area which are symmetric about the crack. The reinforcing effect facilitates crack propagation while the shielding effect inhibits crack propagation.

Mode-I, Mode-II, and Mode-III Stress Intensity Factor Estimation of Regular- and Irregular-Shaped Surface Cracks in Circular Pipes

Stress intensity factor (SIF) of surface cracks (semi-circular, semi-elliptical, and irregular shapes) located on a circular pipe (hollow) has been determined using numerical method. The irregular-shaped crack geometry was considered in the present work in order to simulate the cracks that are generally developed during service condition. The interaction behavior of multiple cracks on SIF calculation has also been investigated. Crack aspect ratios [a/c; “a” is the crack depth and where “c” is semi-major axis of elliptical crack] ranging between 0.6 and 1.0 and crack depth ratios [(a/d); where “d” diameter of the pipe] ranging between 0.1 and 0.4 were considered. Irregular-shaped cracks were modeled by keeping the crack depth (a) constant. For a regular profile semi-elliptic crack [(a/c) = 0.6], higher SIF was observed at crack middle region [(S/S0) = 0]. In contrast, higher SIF was observed at crack surface region [(S/S0) = ± 1] for semi-circular crack. Asymmetric spreading of SIF was noticed because of added effect of mode-II and mode-III fracture. In addition, the leading mode of fracture at short crack depth [(a/d) ≤ 0.1] was mode-II (in-plane shear) and mode-III (out of plane shear) fractures whereas at deep crack depths [(a/d) ≥ 0.4], the leading mode of fracture was mode-I fracture which is crack opening mode. Marginal influence of crack aspect ratio was noticed at crack surface region [(S/S0) = ± 1] and the effect is significant at crack middle region [(S/S0) = 0]. For a constant crack depth, higher SIF was obtained at the middle region [(S/S0) = 0] compared to regular profile crack. When comparing the observations of regular semi-elliptic crack, higher influence of mode-II and mode-III fracture was observed for irregular-shaped semi-circular crack which may leads to additional crack growth. Thus, approximating the standard crack geometry may over/under predict the SIF values. It is also inferred that the presence of adjacent cracks significantly affects the SIF of middle crack due to interaction effect. The interaction behavior was observed to be more pronounced when multiple cracks are located at closer interval. The interaction effect reduces gradually when the distance between crack centers increases. The improved SIF solutions obtained with consideration of additional fracture modes will be useful during the residual life determination.

Stress intensity factors of a Griffith crack in a porous medium subjected to a time-harmonic stress wave

In many practices, cracks are filled with fluid and their background materials can be modelled within the framework of poroelasticity. Understanding the crack-tip mechanical behaviors of such a cracked medium subjected to dynamic loads is of importance for prediction of fracture failure. In this paper, based on Biot’s theory of poroelastodynamics, solutions of mode-I and mode-II dynamic stress intensity factors (SIFs) of a Griffith crack are derived for the scattering problem of oblique incidence of in-plane time-harmonic P-SV waves. The crack surfaces are assumed to be permeable, and the crack is saturated by fluid. With the aid of Fourier integral transforms, the problem is reduced to a system of coupled Fredholm integral equations with special emphasis placed on finding the near-field solution. Impacts of incident wave type, material permeability and incident angle on the frequency-dependent behaviors of the SIFs have been shown graphically. It is found that the induced fluid pressure inside the crack can significantly change the effective normal stress so that the magnitude of mode-I SIF is much lower than that of a dry impermeable crack. Furthermore, the diffusion-type fluid flow (scattered slow P wave) can greatly lower the magnitude of mode-I SIF at low frequencies (much smaller than the resonance frequency). The characteristic frequency at which the curves of SIFs decline strongest occurs when the characteristic diffusion length is of the same order of the crack size. The fluid flow can also lower mode-II SIF at low frequencies and the effects are strong in the low permeability case. Specifically, in the case of scattering of SV waves, it is shown that the maximum drop of mode-II SIF in peak with respect to that of the corresponding dry crack in an elastic medium is about 10%. The obtained results reveal significant influences of the presence of pore fluid upon the SIFs, both magnitudes and frequency-dependent trends. Such information is useful in predicting the fracture strength of saturated porous materials subjected to oscillating loads.

A Numerical Study of Creep Crack Growth in an Aero-engine Turbine Disc using XFEM

In this paper, a turbine disc of an aero-engine having a macro crack under creep loading is studied to predict the creep crack growth. Extended finite element method (XFEM) is used as it does not require conformal meshing and remeshing due to change in the topology during crack growth. The elasto-plastic behavior of the material is modelled by Ramberg-Osgood model and von-Mises yield criterion. The creep behavior is modelled by coupling of spatial and temporal dimensions to capture the effect of stress relaxation and redistribution due to creep strain. The creep crack growth rate is computed by the C(t)-integral which includes small-scale creep, transition creep and extensive creep. The crack growth direction is estimated by the maximum principal stress criterion using mode-I and mode-II stress intensity factors (SIFs). The interaction integral approach is implemented for the evaluation of stress intensity factors of different modes. The history fields of plasticity and creep are transferred properly from the old configuration to new configuration after the crack growth which is the main challenge in this analysis. This proposed numerical scheme is then utilized to obtain the creep crack growth in the component made of elasto-plastic-creeping material. The creep crack growth variation with time is estimated by the XFEM to evaluate the life of an aero-engine turbine disc under creep conditions.

Rolling disc model for rock cutting based on fracture mechanics

A rock cutting by a TBM's rolling disc model based on Linear Elastic Fracture Mechanics is considered in this study. From dimensional considerations the factors that primarily influence the normal force exerted by disc cutter mounted on the cutterhead of a rock TBM are: (i) the fracture toughness of the rock itself that controls the propagation of a critical initial crack leading to chipping, (ii) the disc's tip shape that also influences the ratio of normal force to the lateral force and the ratio of the normal force to the rolling force, and (iii) the disc's penetration depth that also depicts together with the disc radius the contact area, and (iv) the spacing between adjacent cuts. The hardness of the rock is then calculated by dividing the normal force with the contact area. These parameters are considered here as the main input parameters for the simulation of the quasi-static propagation of a lateral crack that gives a rock chip starting from the disc towards the adjacent kerf created by the neighboring cutter under the action of a concentrated load. In this first order approach we assume that the size of the starter crack over the penetration depth ratio remains constant. For the accurate computation of the mode-I and mode-II stress intensity factors at each crack growth increment, we have employed the displacement discontinuity numerical method equipped with a special crack tip element based on strain gradient or grade-2 (g2) elasticity theory. Mixed-mode crack growth obeys either the energy balance criterion or maximum tangential tensile stress criterion. The numerical results are then compared with published linear cutting rig test results on four rock types. The accuracy of the maximum tensile tangential stress criterion is better compared to the energy balance criterion. However, even with the simplest self-similar crack growth fracture criterion based on energy balance, we have found acceptable agreement of numerical with experimental results by assuming only one free parameter, namely the mode-I fracture toughness of the rock. It is thus recommended that the rock characterization for disc cutting processes should be done not only by the uniaxial compression and indirect tension tests, but also with a proper fracture mechanics test according to the ISRM Suggested Methods for the determination of the rock fracture toughness.

A theoretical model for hydraulic fracturing through a single radial perforation emanating from a borehole

This paper considers the problem of the plane-strain fluid-driven fracture propagation of a single radial perforation emanating from a borehole. A maximum tangential strain criterion is proposed to study crack propagation during hydraulic fracturing; this criterion considers the changes in not only the mode-I stress intensity factor caused by the pore pressure but also the mode-II stress intensity factor caused by the anisotropy of the far-field stress. The critical water pressure and the critical initiation angle at the onset of crack propagation are studied using the proposed theoretical method. The effects of the stress anisotropy coefficient, the borehole radius, the perforation length, the ratio of the water pressures inside the fracture to that of the borehole, Biot’s coefficient and Poisson’s ratio on both the critical water pressure and the critical initiation angle are discussed. The parameter analysis indicates that the perforation length, the borehole radius and the stress anisotropy coefficient significantly affect the critical water pressure and the critical initiation angle. The critical water pressure decreases as the ratio of the water pressure inside the fracture to that of the borehole and Biot’s coefficient increase, whereas the critical initiation angle is not affected by these parameters. The critical water pressure increases and the critical initiation angle decreases as the Poisson’s ratio increases. During high-pressure water injection, the fracture initiation angle decreases with increases in the water injection pressure, Biot’s coefficient and the ratio of the water pressure inside the fracture to that of the borehole; however, the angle is not affected by Poisson’s ratio. The theoretical model provides a comprehensive understanding of the characteristics of hydraulic fracturing under complex loading conditions. The results also provide a basis for quantitative investigations of the engineering design of hydraulic fracturing treatments.

Nonlinear Fatigue Crack Growth Simulations using J-integral Decomposition and XFEM

In the present work, nonlinear fatigue crack growth analysis of an inclined edge crack is performed by extended finite element method (XFEM) [1]. The material behavior is assumed to be nonlinear, which is modelled by Ramberg-Osgood model and von-Mises yield criterion. Due to inherent material nonlinearity, the interaction integral approach cannot be used for evaluating the individual stress intensity factors (SIFs). Hence, the mixed mode crack growth problem is solved by decomposing the mixed mode J-integral into mode-I and mode-II. The decomposition of stress, strain and displacement fields is done by considering the symmetric and anti-symmetric parts of the corresponding field [2]. The symmetric part of these fields is related with the symmetric part of J-integral and provides mode-I SIF (KI) whereas the anti-symmetric part of these fields provides the mode-II SIF (KII). The equivalent KI and KII are used to find the direction of crack growth and the equivalent effective KIeq for the obtained direction of the crack growth. The range of KIeq (ΔKIeq) is used with the Paris law to evaluate the rate of crack growth. For highly nonlinear materials, J-integral decomposition method is more suitable then interaction integral approach.